If a value grew by P% to reach V, find the original base: V ÷ (1 + P/100).
It solves base × (1 + p÷100) = value, so base = value ÷ (1 + p÷100). Validation requires p ≥ 0 and value ≥ 0, and rejects p ≤ −100 (would break the divisor)—so on this page only non‑negative markups are accepted.
This calculator uses plain decimal numbers. If a result looks wrong, check whether you used a comma instead of a dot (or vice versa) where the field expects one.